Bug 1036928 - Allow to set longer time estimages as 60 minutes

Closed the previous pull- working only on this branch now.
This form doesn't really look the way we want it to. Imagine you are a user of the system - would you understand how this works? What is `Admin time`, and how does it relate to `Estimated time`? I think what we need is to display the `admin_time` field immediately beside the select box for `execution_time` and display a hint to tell users what it's for. We'll also need to add an option to the select box for `---` so that people aren't choosing a time and also typing in a value, as that doesn't really make sense. We'll also need to add logic to make sure that a user has either selected a value for `execution_time` *or* entered a value for `admin_time`.